NanoSIMS element mapping and sulfur isotope analysis of Au-bearing pyrite from Lannigou Carlin-type Au deposit in SW China: New insights into the origin and evolution of Au-bearing fluids

摘要

Graphical abstractThe Carlin-type gold deposit is best known in Nevada (USA) and SW China. In this paper, we report detailed field geology and mineral geochemical studies of gold-bearing pyrites from Lannigou Carlin-type Au deposit, SW China. Geological observations indicate that Lannigou Au deposit is a sediment-hosted gold deposit with quartz veins and controlled by steeply-dipping NW-trending F3, F6 fault and the intersection of F3 fault and NE-striking F2 fault, or secondary faults. As the main host mineral, arsenic pyrite is characterized by core-rim structure. And there is significant zonation in pyrite rim. EPMA data shows that core is characterized by low As, Au, Cu and higher Ni concentration. In contrast, rim has elevated concentration of As, Au and Cu. NanoSIMS mapping reveals the zonation of elements distribution including As, Au and Cu. According the textures and distributions of As and Au, we recognized three main stages of pyrites and late stage sulfides. Stage 1 pyrites were formed prior mineralization process. Stage 2, arsenic pyrites precipitated without Au. Stage 3, main Au precipitation taken place. Line scan of pyrite rims reveal that the peaks of As and Au were coupled with valley of δ34S in stage 3a and the correlations between As and Au are different in stage 3a and 3b. These observations indicate that Au precipitation mainly caused by fluid mixing. S isotope analyzed by NanoSIMS reveals a mixing trend between a magmatic-related fluid with δ34S value about 0‰ and a basin fluid with δ34S value about 18‰.Display OmittedHighlights?The distribution of ore-related elements and δ34S across individual pyrite crystals, from representative Carlin-type gold deposit in SW China, are determined by NanoSIMS.?The complex Au-As relationships revealed by NanoSIMS indicate multiple mechanisms of Au precipitation during mineralization.?The significant variation of δ34S value across individual pyrite grains reveal a mixing process of hydrothermal ore fluids. One of the origin could be trace element enriched fluid with mantle-like δ34S and another is a crustal fluid with elevated δ34S.AbstractSulfur isotope signatures of Au-bearing pyrite from Lannigou Au deposit, a typical Carlin-type Au deposit in SW China, provide valuable information about the origin of the ore-forming minerals. Analysis by NanoSIMS was used to determine S isotope compositions of Au-bearing pyrite and to map the grain-scale distributions of Au, Cu, As an